Method and means for producing photo-electric tubes



July 2, 1935. s. WEIN 2,006,850

METHOD AND MEANS FOR PRODUCING PHOTO-ELECTRIC TUBES Filed July 7, 1950 FZ'ne grc zllned alkalimelal hydride INVENTOR Samuel -WeLn WATTORNEY 5L Patented July 2, 1935 UNlTED STATES METHOD AND MEANS FOR PRODUCING PHOTO-ELECTRIC TUBES Samuel Wein, New York, N. Y., assignor, by mesne assignments, to Radio Corporation of America, a corporation of Delaware Application July '7, 1930, Serial No. 466,037

2 Claims.

This invention relates to light sensitive devices and' 'with particularity to photo-electric tubes such as employed in television, picture transmission, sound reproducing and similar systems.

An object of the invention is to provide a novel method of preparing photo-electric tubes.

Another object of the invention is to provide a photo-electric tube having a greater sensitivity than the tubes produced by prior art methods.

Another object of the invention is to provide a photo-electric tube having a minimum of polarization in the surface of the light sensitive coating.

A feature of the invention relates to the method of utilizing heat to produce an alkali metal hydride coating.

Other features and advantages of the invention not specifically enumerated will be apparent after a consideration of the following detail description and the appended claims.

While photo-electric tubes employing the light sensitive coating of an alkali metal hydride are well known, the present invention is in the nature of an improvement on the method of producing this hydride coating. There is disclosed in United States Patent #l,38l,l7l a method of manufacturing a photo-electric tube having an alkali metal hydride light sensitive coating. In general the method of manufacturing photoelectric tubes as commercially employed is to first provide the major portion of the interior Wall of the tube with a conductive coating of silver or other similar material. The tube with this coating thereon is then evacuated to the required degree and an alkali metal such as sodium or potassium is distilled into the tube interior and is allowed to deposit on the previously deposited conductive coating. During this distillation care must be taken to insure that the alkali metal is not undesirably deposited on other parts of the tube interior. The coating of silver or other conducting material with the alkali metal deposited thereon forms one of the electrodes of the tube while another uncoated member forms the remaining electrode, it being understood that a suitable connection is provided to the light sensitive coating.

In order to render the alkali metal coating more sensitive the usual practice is to pass a certain amount of hydrogen into the tube and to subject the tube to an electric discharge which converts the alkali metal coating into an alkali hydride. It has been found that amaximum sensitivity of the tube is attained when the light sensitive coating is in the form of a finely grained or colloidal surface of alkali metal. a It has'also been found that when the alkali metal hydride is formed by the electrical discharge method of the prior art as described in Patent No. 1,381,47 l that the light sensitive surface is a coarsely; grained colloidal one and has a marked surface polarization. In accordance with the present invention it is proposed to convert the alkali metal coating into a hydride coating by subjecting the hydrogen and the alkali coating to heat. The heat may be applied to either substance. The following is a typical method of preparing the tube which has a very finely grained colloidal light sensitive surface according to the invention. After the tube bulb has been evacuated by any Well known method a conducting film of magnesium is deposited on the interior wall of the tube but a portion of the tube is left uncoated to provide a window for the admission of light to the interior of the tube. This conducting film of magnesium serves as one of the tube electrodes and may be produced either by a flashing or exploding process such as is Well known in the vacuum tube art, or the magnesium may be distilled from a side chamber into the tube proper. If desired, instead of using flashing or distilling operations for the deposition of the magnesium, the magnesium may be provided in the form of a Wire or strip within the tube and volatilized by heat or by the passage of an electric current therethrough.

After the formation of the magnesium coating, metallic potassium, sodium or other alkali metal is distilled into the tube and allowed to deposit upon the film of magnesium, it being understood that the tube is being continuously evacuated during these distillation processes.

After the formation of the coatings of=magnesium and alkali metal the bulb is disconnected from the evacuating pump and a predetermined amount of dry hydrogen is passed into the bulb. The bulb with the hydrogen therein is then heated by any suitable means such as a gas burner, an electric heater or the like, to cause a chemical reaction between the hydrogen and the alkali metal coating whereby all said alkali metal coating is converted into a hydride of the alkali metal which, as is Well known, has the greatest response to light.

After the formation of the hydride the remaining hydrogen is pumped out of the bulb and a filling of inert gas such as argon, neon, helium, etc., is forced into the tube, preferably at a low pressure. The tube is then sealed ofi from the pump and is ready for use.

Instead of heating the hydrogen after it is passed into the bulb to produce the chemical reaction with the alkali metal coating, the hydrogen may be heated prior to its entrance into the bulb with the same efiect, or if desired, dry cold hydrogen may be passed into the bulb and the coating of alkali metal alone heated or the alkali metal may be heated in the presence of hydrogen at the same time that it is being distilled over into the bulb fromthe side tube. 'It being understood that the hydrogen remains heated for a short time after its passage into the bulb.

It has been found that tubes produced in accordance with the above described method possess a maximum sensitivity and exhibit very little, if any, surface polarization.

It is to be understood that the expression tube,.as employed herein is not to be limited to any particular shape of enclosing container since the invention may be obviously embodied in any well known form of enclosing vessel such as employed in the electric discharge tube arts.

What is claimed is:

1. The method of manufacturing a light sensitive cathode which includes the steps of providing a portion of the interior surface of a tube with a coating of alkali metal and bringing heated hydrogen into contact with said coating to form a finely grained coating of the hydride of the alkali metal.

2. The method of manufacturing a photo-electric cathode which comprises evacuating a tube, depositing on a portion of the interior wall of the tube a coating of conductive material, applying a coating of alkali metal to said conductive coating, introducing hydrogen into the tube, producing by heat unaccompanied by a discharge a reaction between the hydrogen and the alkali coating and then removing the excess hydrogen 20 from the tube.

SAMUEL WEIN. 

